The chemical name of Ropinirole is 4-[2-(Dipropylamino)ethyl]-1,3-dihydro-2H-indol-2-one, formula C16H24N2O and molecular weight is 260.37. Ropinirole is marketed in the form of its hydrochloride salt. The current pharmaceutical product containing this drug is being sold by Glaxosmithkline using the tradename Requip®, in the form of tablets. The structural formula of Ropinirole is represented by formula (I)

Ropinirole is useful in the treatment of Parkinson's disease. Ropinirole is a dopamine agonist and having selective affinity for dopamine D2-like receptors and little or no affinity for non-dopaminergic brain receptors. Ropinirole is indicated as adjunct therapy to levodopa in patients with advanced Parkinson's disease. Also, recent clinical trials have focused on its use, as monotherapy in patients with early Parkinson's disease.
A process for preparing Ropinirole hydrochloride is set forth in U.S. Pat. No. 4,452,808 which is a product patent of Ropinirole. In this patent the Ropinirole hydrochloride was prepared by catalytic hydrogenation of 2-nitro-6-(2-di-n-propylaminoethyl)-phenyl acetic acid hydrochloride in the presence of 5% palladium on carbon in ethanol. The product was crystallized from hot acetonitrile. However, in this patent the volume of acetonitrile taken for purification is 400 times to that of the crude compound taken. This increases the overall cost of the production. Moreover, such kind of purification is not feasible on industrial scale.
J. Med. Chem. 1985, 28, 1533-1536 and J. Med. Chem. 1986, 29, 939-947 also disclose the purification of Ropinirole hydrochloride by crystallization of crude from hot acetonitrile.
U.S. Pat. No. 4,997,954 discloses the purification of Ropinirole hydrochloride by recrystallization from isopropanol or basification and re-acidification procedures to give a product of 98-99% purity.
WO2005080333 discloses a purification process for Ropinirole hydrochloride by forming imine derivative. The process comprises the steps of    (a) dissolving or suspending crude ropinirole base or its pharmaceutically acceptable salt in a suitable solvent,    (b) reacting the solution or suspension of step (a) with a nitrogenous base to form an imine derivative,    (c) optionally treating the reaction mixture of step (b) with a suitable base to adjust the pH between 9 to 14,    (d) isolating purified ropinirole hydrochloride.
The nitrogenous base is selected from the group comprising of hydroxylamine hydrochloride, hydrazine hydrate, and phenyl hydrazine.
Hydroxylamine hydrochloride is corrosive, causes burns to any area of contact. It is harmful by inhalation, ingestion or skin absorption. It is extremely destructive of mucous membranes, upper respiratory tract, eyes and skin. It cause severe irritation and corneal damage to eye. On injestion, it converts hemoglobin to methemoglobin, producing cyanosis. It also cause nausea, vomiting, fall in blood pressure, headache, vertigo, ringing in the ears, shortness of breath, severe blood oxygen deficiency and convulsions. High concentrations cause coma and death from circulatory collapse. On chronic exposure it causes anemia, weight loss, nervous system affects, and kidney, liver and bone marrow damage.
Phenyl hydrazine is corrosive. It is harmful if swallowed, inhaled or absorbed through skin. It is suspected as carcinogen and cancer hazard. It is poisonous. On inhalation it causes irritation to respiratory tract. On skin contact, it causes burns to any area of contact and lead to dermatitis and skin sensitization. It affects blood, liver, kidneys and respiratory system. It may cause vomiting, dizziness, faintness, and jaundice.
WO2005105741 discloses a purification process for Ropinirole hydrochloride by treating Ropinirole free base with a reducing agent and then converting it to pure Ropinirole hydrochloride. The reducing agent is selected from sodium metabisulfite, sodium hyposulfite, sodium hydrosulfite, hydroxylamine, hydrazine or mixtures thereof.
Sodium hyposulfite is harmful by ingestion, inhalation, or skin absorption. It is irritant on Acute Exposure. It may irritate or burn eyes and cause temporary conjunctivitis. It causes skin irritation. Dust or mist may cause severe irritation to the respiratory tract. Exposure may cause coughing, chest pains and difficulty in breathing. If it is heated to the point where sulfur dioxide gas is driven off, then this gas is highly irritating to the respiratory tract. It causes gastrointestinal irritation such as nausea, vomiting, purging and cyanosis.
Hydrazine is toxic, and may be fatal, if inhaled, swallowed or absorbed through the skin. It is expected to be a human carcinogen. The substance is toxic to blood, kidneys, lungs, the nervous system, mucous membranes. Long-term exposure may cause CNS, lungs, blood, liver and kidney damage. It is highly corrosive and may produce tissue damage particularly on mucous membranes of eyes, mouth and respiratory tract. It is animal embryotoxic. Severe over-exposure can result in death.
Sodium metabisulfite is harmful if swallowed or inhaled. It causes irritation to skin, eyes and respiratory tract. It reacts with acids and water thereby releasing toxic sulfur dioxide gas which is harmful and deadly if inhaled which may cause severe or deadly allergic reactions in some asthmatics and sulfite sensitive individuals. Very large doses of intake may cause violent colic, nausea, vomiting, diarrhea, abdominal pains, circulatory disturbance, and central nervous system depression and even death. It may cause irreversible eye damage to eye such as stinging, tearing, redness, swelling, corneal damage and blindness.
In summary, prior art relating to the process for the preparation of Ropinirole hydrochloride suffers with several drawbacks such as use of very toxic and hazardous reagents.
It is therefore a need to develop an improved process for the purification of Ropinirole hydrochloride which not only overcomes the aforementioned problems but also provide a process which is simple, easy to perform and feasible at commercial production.
The present inventors have directed their research work towards developing an improved process for the preparation of Ropinirole hydrochloride. The present inventors focused their research work towards improving the colour of final product thereby removing coloured impurities. The present inventors used various bleaching agents as well as active carbon such as charcoal on which the metal impurities imparting colour are adsorbed. The present inventors unexpectedly found that sodium dithionate acts effectively as bleaching agent unlike other bleaching agents such as sodium bisulfite and sodium metabisulfite. The present inventors also used trituration techniques to further purify the product. The present inventors thus invented an improved process which provides Ropinirole hydrochloride with improved yield and purity having more than 99%.